Question

How many moles are in 20.0 g of water

Answer 1

Mass = mr x moles

Therefore we rearrange to get

Moles = mass/ mr

Water is H2O so the molecular mass values are
H: 1 , O: 16 (from the periodic table).

We have 2 Hs and 1 O so 1 + 1 + 16 = 18

Mass/ mr = 20/18 = 1.11 moles of water

Hope this helps, feel free to ask if you have any questions :)